1. Field of the Invention
The present invention relates to a lens drive controller, and specifically relates to a lens drive controller suitable for zoom lens systems which electronically correct movement of the focal plane during zooming and which is provided with a device to correct image blur caused by camera movement or vibration, and apparatus provided with such drive controller.
2. Description of the Related Art
In zoom lens systems used in cameras and the like, the focal plane shifts as the focal length of the lens changes during the zooming operation. Therefore, in conventional zoom lens systems, focal plane shift is corrected by moving a focusing lens unit via a cam mechanism simultaneously with the operation that changes the focal length by moving the zooming lens unit via a cam mechanism, such that there is no shifting of the focal plane by the zooming operation.
The aforesaid construction, however, uses a plurality of cams of complex configuration, which is disadvantageous insofar as it enlarges and complicates the overall structure of the zoom lens system. To resolve these disadvantages, an electronic correction process has been proposed, that is, a central processing unit (CPU) provided in a zoom lens system calculates the amount of correction required to correct focal plane shifting caused by a zooming operation, and driving a focusing lens unit based on said calculation result.
In such electronic correction, the distance between the focal length at the wide angle end of the zoom lens element and the focal length at the telephoto end thereof is divided into a plurality of zones in advance. Then, electronic correction treats the change in focal length of the zoom lens system caused by a zooming operation as movement from one zone to another zone, and has pre-stored in memory various correction information for correcting focal plane shift related to each zone.
When a change in focal length of the zoom lens system (i.e., movement from one zone to another zone) is detected, a determination is made as to whether or not the shift in the focal plane requires correction based on the focal length information after said change and the current position information of the focusing lens unit. When the result of the aforesaid determination is that the focal plane shift must be corrected, the amount of movement of the focusing lens unit to achieve said correction is calculated based on the focal length information after said change, the current position information of the focusing lens unit, and correction information for correcting focal plane shift previously stored in memory, whereupon the focal plane shift is then corrected by moving the focusing lens unit by the calculated amount of movement.
In conventional zoom lens systems using cam mechanisms, a user can normally confirm the focused photographic object without a sense of unease because the focal plane shift is corrected without temporal delay by simultaneously moving the focusing lens unit via a cam mechanism and moving the zoom lens unit via the zooming operation. In electronic correction, however, a user may have a sense of unease unless the focusing lens unit rapidly tracks the zooming operation since the lens element CPU starts the calculation process in response to the zooming operation.
On the other hand, a correction method has been proposed wherein a blur correction lens unit is provided used in a lens system or used in a camera, so as to correct image blur caused by vibration of the camera by detecting shaking (movement) of the camera resulting from the hand shake of the operator, and driving the blur correction lens unit accordingly. Since this type of lens system and this type of camera are constructed so as to execute the zooming operation, focus detection, and exposure control and the like using a battery as a power source, the load on the battery is increased, as well as the load for calculations performed by the CPU.
Therefore, when accomplishing blur correction during a zooming operation, disadvantages arise inasmuch as there is a reduction in correction response speed to the focal plane shift, and the camera operator does not receive an excellent sense of the operation.